This invention relates to a heat exchanger for exchange of thermal energy from one substance to another. The heat exchanger is particularly useful for a variety of fluids including gases and liquids and is particularly suitable for high pressure systems and systems requiring periodic cleaning because of scale of surface fouling. The heat exchanger of this invention is primarily related to a double pipe heat exchanger in which a first pipe is concentrically positioned within a second pipe and one fluid flows through the inside pipe and the second fluid through the annular space between the outside and the inside pipe. The double-pipe heat exchanger is a simple system to construct and is capable of operating at relatively high pressures because of the generally moderate diameter of the outer pipe compared to the diameter of the outer shell of a multitube exchanger. However, the limited surface area renders the double-pipe system inadequate for most heat exchange situations. Further, the uniform annular and uniform circular cross sections of the fluid conduits promote laminar flow which characteristically inhibits effective transfer of heat from one fluid to the other. While multiple tube heat exchangers provide a substantial increase in surface area for component length, the shell encasing the tubes must be specially fabricated to contain and support the bundle of tubes at customary operating pressures, usually in excess of 150 psi. Further, such multiple tube heat exchangers are difficult to service for cleaning or repair and are expensive to fabricate. While baffles are frequently provided within the shell to direct the flow of the fluid outside of the tubes back and forth across the tubes, the heat transfer area is limited to the surface area of a tube multiplied by the number of tubes in the tube pack.
The straight tube heat exchanger of this invention is particularly useful in conjunction with a boiler and deaerator for condensing return steam and preheating boiler supply water. When used in an array of two or more exchangers the devised heat exchanger array uniquely permits steam return at multiple different temperatures often encountered in various manufacturing processes. This solves the vexing problem of multiple steam circuits each requiring its own pressurized receiver and high pressure pump for return of the condensate to the boiler. These and other features are described hereafter.